How Ancient Humans Walked: Their Footprints May Mislead

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Fossil footprints could provide a skewed view of how ancient
animals — including early human ancestors similar to the famous
Lucy fossil — walked, new research suggests.

In the past, paleontologists and anthropologists assumed the
depth of the footprint correlated with the pressure used to
create it. But the analysis, published today (March 19) in the
Journal of the Royal Society Interface, reveals that the heel
tends to create a deeper indentation even when applying the same
amount of pressure.

"We shouldn't necessarily expect the shape of a footprint to
directly reflect the way the animal that made it walked," said
study co-author Karl Bates, a biomechanics researcher at the
University of Liverpool in the United Kingdom.

But deciphering the
ancient marks to recreate human ancestors' gait is tricky.
Historically, scientists assumed the depth of the indentation
directly correlated with the pressure placed at that spot. But
testing that experimentally was difficult, as the force plates
that measure foot-strike pressure are made of materials that
don't deform and leave footprints.

To get a more thorough look, Bates and his colleagues created a
computer model that simulated the pressure of various sizes of
feet as they depressed different types of soils with various
strikes.

They then asked 10 people to walk along the beach in Brighton, on
the south coast of Great Britain, and measured their footprints.
The same people then walked on a force-measuring treadmill, and
the researchers correlated the footprint depth with pressure
during walking.

Both methods found similar trends: different parts of the foot
create different size indentations even when
striking the ground with the same amount of pressure.

"The heel is a more effective indenter than the forefoot and the
toes," Bates told LiveScience.

The softer the walking surface, the more exaggerated this effect.

While the researchers focused on human gait, the new analysis
should also apply to
dinosaur prints and other extinct animal tracks, Bates said.

Ancient walkers

The study is impressive because it cleverly combined
sophisticated computer models and experimental approaches, said
Kristiaan D'Août, a biomechanics researcher at the University of
Antwerp who was not involved in the study.

"They're two totally different techniques, but they both yielded
overall rather similar results," D'Août told LiveScience.

The findings suggest there's a much more complicated relationship
between foot pressure and footprint depth, which could force
scientists to rethink their past assumptions about the gaits of
early human ancestors, he said.